The present invention relates to LHRH antagonist peptides and uses thereof.
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are hormones released by the pituitary gland. These hormones regulate the functioning of the gonads and the production and maturation of gametes. LH and FSH are generally released by the pituitary gland upon prior release of triggering hormone from the hypothalamus. Luteinizing hormone-releasing hormone (LHRH; also known as gonadotropin-releasing hormone or GnRH) is one of the principal hypothalamic hormones which triggers the release of LH. Thus, release of LHRH represents a control point in the physiological regulation of gonadal function. The structure of mammalian LHRH has been determined, and has been found to be a decapeptide: 
LH release is necessary for ovulation; thus, compounds which inhibit LH release by blocking the action of LHRH are useful as contraceptive agents. LHRH antagonists are also useful for regulating secretion of gonadotropins in male mammals, and thus can be used as male contraceptives. In addition, LHRH antagonists can be used in the treatment of sex-hormone dependent cancers (for example, prostate cancer), where increased levels of gonadotropins increase the rate of tumor growth.
Many modified LHRH analog peptides have been synthesized in an attempt to increase the potency of the antagonists, preferably while also increasing the resistance of the antagonist to enzymatic degradation. For example, synthetic LHRH antagonist peptides which incorporate modified or unnatural amino acids have been tested. Common substitutions include, for example, substitution of 4-Cl-D-Phe for His at position 2, or substitution of D-Ala-NH2 for Gly-NH2 at position 10.
One problem frequently encountered in LHRH antagonist peptides is the occurrence of histamine-releasing activity. This histamine-releasing activity represents a serious obstacle to the clinical use of such antagonists because histamine release results in adverse side effects such as edema and itching. Thus, LHRH antagonist peptides which have low histamine releasing activity are particularly desirable. Although the LHRH antagonist and histamine-releasing properties are not necessarily related, very few prior art compounds combine low histamine-releasing activity with high LHRH antagonist activity. Many prior art LHRH antagonist peptides also suffer from poor water-solubility, which complicates formulation of the antagonist for administration.
The present invention features LHRH antagonist peptides, methods of modulating LHRH activity, and methods of treating a subject with the antagonists of the invention. In one embodiment, an LHRH antagonist comprises a peptide compound, wherein a residue of the peptide compound corresponding to the amino acid at position 6 of natural mammalian LHRH comprises D-Lys(Imdac), D-Lys(Ppic), D-Lys(Dodac), D-Lys(pGlu), D-Lys(Otac) and D-Lys(Onic) or a moiety selected from the group consisting of a dipolar moiety, a sulfonium moiety, a receptor-modifying moiety and a small polar moiety, such that the peptide compound has LHRH antagonist activity, with the provisos that the dipolar moiety is not a zwitterionic pyridinium and the residue is not D-Cit, D-Hci or a lower alkyl derivative of D-Cit or D-Hci. Preferably, the peptide compound comprises about 8 to about 12 residues. More preferably, the peptide compound comprises 10 residues.
In another embodiment, the invention provides a peptide compound comprising a structure:
A-B-C-D-E-F-G-H-I-J
wherein
A is pyro-Glu, Ac-D-Nal, Ac-D-Qal, Ac-Sar, or Ac-D-Pal;
B is His or 4-Cl-D-Phe;
C is Trp, D-Pal, D-Nal, L-Nal, D-Pal(Nxe2x80x94O), or D-Trp;
D is Ser;
E is N-Me-Ala, Tyr, N-Me-Tyr, Ser, Lys(iPr), 4-Cl-Phe, His, Asn, Met, Ala, Arg or Ile;
F is D-Lys(Imdac), D-Lys(Ppic), D-Lys(Dodac), D-Lys(pGlu), D-Lys(Otac), D-Lys(Onic) or a structure: 
xe2x80x83wherein
R and X are, independently, H or alkyl; and
Y comprises a moiety selected from the group consisting a dipolar moiety, a sulfonium moiety, a receptor-modifying moiety and a small polar moiety, the provisos that the dipolar moiety is not a zwitterionic pyridinium and F is not D-Cit, D-Hci or a lower alkyl derivative of D-Cit or D-Hci;
G is Leu or Trp;
H is Lys(iPr), Gln, Met, or Arg;
I is Pro; and
J is Gly-NH2 or D-Ala-NH2;
or a pharmaceutically acceptable salt thereof.
The invention also provides pharmaceutical compositions of the LHRH antagonist peptides.
In another aspect, the invention provides a method of inhibiting LHRH activity in a subject, comprising administering to a subject an effective amount of an LHRH antagonist, such that LHRH activity is inhibited.
In another aspect, the invention provides a method of inhibiting LHRH activity in a cell, comprising contacting a cell with an LHRH antagonist, such that LHRH activity is inhibited.
In another aspect, the invention provides a method of inhibiting growth of a hormone-dependent tumor in a subject, comprising administering to a subject an effective amount of an LHRH antagonist, such that tumor growth is inhibited.
In another aspect, the invention provides a method of inhibiting ovulation in a subject, comprising administering to a subject an effective amount of an LHRH antagonist, such that ovulation is inhibited.
In another aspect, the invention provides a packaged formulation for treating a subject for a disorder associated with LHRH activity, comprising an LHRH antagonist packaged with instructions for using the LHRH antagonist for treating a subject having a disorder associated with LHRH activity.